It has probably been done before ; ( although I can't find anything about it with the search engine on this forum ) ...And Phil at RCtankwars is selling a tensioner design that seems quite sturdy ( also pricy ....) .
But since I'm cheap and I have an old non smoke & sound Pershing that I keep for spare parts ; I decided to take a shot at it ....
I tried to keep the tensioner very simple and self-adjusting ...
Here's a bunch of pictures with commentaries ....